It is useful in a variety of instances to detect the location of an article. One way to do so is to place an identification device on or within the article, and sense the location of the identification device by its interaction with an electromagnetic field generated by a reader device. Appropriate electrical and/or mechanical devices engaged with the identification device and/or reader can then accomplish a desired task. As an example, an identification device can be attached to a garment or other article for retail sale for the purpose of activating an alarm if the article is improperly removed from a retail store. As another example, an animal may be tagged with such a device so that its movement into or out of a given area can be monitored. As another example, a vehicle key could be provided with such a device so that the vehicle unlocks as the key bearer approaches the vehicle. In general, the identification device is not only used for detection per se, but also to read information from and write information to the reader device. As another example of an application that may be particularly useful for the present invention, an identification device could be placed into a branded good to ensure the genuineness of the good as is passes through trade channels (i.e., prevention of counterfeit goods). A reader device at a retail location could ensure that tendered goods are genuine by reading an encrypted code stored within an identification device.
The ability of the identification device to store and manipulate information, and transmit the information to the reader device, greatly enhances the potential applications. The present invention may have application to relatively large goods, such as articles of clothing, and also to relatively small goods, such as watches or jewelry. RFID has many other uses and it is expected that still more uses will be developed. It is important for the development of the technology that RFID devices be manufactured inexpensively, and still maintain good performance characteristics.
An RFID device can be considered to have two primary components: an antenna and an integrated circuit (IC). The IC includes circuitry to interface with the antenna, encoder and decoder logic circuitry, signal processing circuitry, memory, and possibly other functions. The memory is generally nonvolatile memory, e.g., flash memory or ferroelectric memory. The memory is usually of small size, such as several hundred bits, although any size memory could theoretically be used.
The IC usually includes a coupling capacitor for transmitting energy from the electromagnetic field generated by the reader to the IC (this capacitor may also be referred to as a storage capacitor). The antenna, commonly a coil type, interacts with the electromagnetic field and is electrically interconnected with the IC. Generally, the antenna is tuned to the frequency of the reader device with which the antenna is intended to be used. Typical frequencies are 125 kHz or 13.56 MHZ. A tuning capacitor is used to provide an identification device oscillation frequency corresponding to the reader frequency. Typical capacitance values are on the order of picofarads or nanofarads.
Since IC and coil technologies are generally unrelated to one another, there has been no way to efficiently manufacture and attach the two components. A standard prior art RFID device as shown in FIG. 1 comprises an IC chip 2, a coil (antenna) 4, and connections (electrical wiring) 6 therebetween. The chip 2 generally has a coupling capacitor 8 formed thereon. While IC manufacturing techniques are quite efficient, the additional steps of manufacturing the coil and connecting it the IC chip fails to exploit these efficient manufacturing techniques. More specifically, IC's are generally manufactured using batch processing techniques, wherein numerous devices are formed simultaneously by following defined procedural steps. Other manufacturing techniques generally require components to be formed one at a time, which is both more expensive and less reliable than batch processing. An aspect of the present invention is the fabrication of an RFID device antenna through batch processing.
Attempts have been made to form a one chip RFID device by integrating the coil and the chip (a "Coil on Chip" or COC). See Glasser, "A Magnetic Power and Communication Interface for a CMOS IC", IEEE J. of SSC, Vol. 24, No. 4, August 1989. Such a COC is not believed to have been commercially successful. Similar devices are described in U.S. Pat. Nos. 4,724,427, 4,857,893, and 5,070,317. The primary antenna performance measures are inductance (L), and a Quality factor (Q) which is a ratio of reactance to resistance. The known COCs have provided unsatisfactory low inductance L and poor Q.
Wafer stacking technology has been developed by the instant inventor and others that allows for a number of wafers to be stacked above one another and electrically interconnected to form an operative unit. See U.S. Pat. No. 5,229,647. Such patent describes wafer stacking techniques of general applicability, but does not suggest adapting wafer stacking techniques to form an operative antenna or otherwise adapting wafer stacking techniques to the unique problems of fabricating simple, economical, and reliable RFID devices. It is a general purpose of the present invention to provide such an RFID device.
Each of the documents referred to herein are hereby incorporated by reference to the extent they include information helpful to a proper understanding of the present invention; the file wrappers of any patent documents are also incorporated by reference. It should be understood that no documents or descriptions herein are admitted to be "prior art," but are only mentioned to place the invention in context and to assist in a proper understanding of the invention.